For an application that requires a higher sealing property that does not allow a permeation leakage like a high vacuum application and a heat resistance property to a baking processing for degassing or the like, a metal gasket made of a soft metal material provided with the excellent sealing and heat resistance properties is used in general rather than a material made of a rubber or an elastomer.
In order to ensure a stable sealing property by using a metal gasket as described above, a tightening force must be extremely enlarged as compared with the cases of a rubber and an elastomer. As a result, in the case in which a metal gasket is used, a strain of a tightening work is increased and a fastening substance such as a flange and a bolt grows in size most commonly.
Moreover, in the case of a gasket in an O-ring shape, that is, a gasket that is not in a sheet-like shape, the gasket is used in general in the state in which the gasket is tightened in a gasket mounting groove when the gasket is mounted. On the other hand, in the case of a gasket made of a rubber or an elastomer in an O-ring shape, the gasket is greatly deformed by a low tightening load. Consequently, in the state in which a bolt is tightened in a stepwise manner, a bolt can be easily rotated and tightened when the gasket is tightened. On the other hand, in the state in which a bolt is attained to be tightened in a groove, the bolt cannot be rotated in a timely fashion or the bolt is rotated hardly.
Consequently, in the case of a gasket made of a rubber or an elastomer in an O-ring shape, it is easy to manage a tightening of a bolt even by a manual work.
On the other hand, in the case of a gasket made of metal in an O-ring shape, a large force is basically required to deform the gasket, whereby it is hard to find a change of a moment when a bolt is tightened to a groove. Therefore, it is hard to manage a tightening of a bolt by a manual work unfortunately.
As a gasket made of metal in an O-ring shape, a metal hollow O-ring and a metal C-ring provided with a spring are also known. Even in the case of a metal hollow O-ring and a metal C-ring provided with a spring, it is hard to find a change of a moment when a bolt is tightened, whereby it is hard to manage a tightening of a bolt by a manual work unfortunately. Moreover, in the case of a hollow metal O-ring and a metal C-ring provided with a spring, the rings can be easily deformed by modifying a wall thickness or a dimension of a part that specifies the entire shape such as “O” and “C”. Moreover, in the case of a metal C-ring provided with a spring, the ring can be easily deformed by properly modifying a thickness of a spring that is installed in the ring. However, in the case in which a thickness of a spring is modified, a reaction force or a stress of a seal face is degraded, whereby a sealing property is also degraded unfortunately.
A wide variety of proposals have been carried out in order to improve a sealing property for a hollow metal O-ring and a metal C-ring provided with a spring.
For instance, a soft layer (such as a metal plate and a rubber coating) is disposed on a seal face of a metal gasket, or a shape that causes a concentration of stress on a seal face of a metal gasket is adopted. In other words, to adopt a shape that causes a concentration of stress, a projecting portion is formed on a seal face in Patent document 1, and a concave groove is formed on a seal face in Patent document 2.
However, even by the above ideas for an improvement, a sealing property cannot be displayed to a satisfactory extent by a smaller tightening force.
Moreover, in the case in which a shape that causes a concentration of stress on a seal face is adopted like the Patent documents 1 and 2 in particular, a flaw may be remained on a face of a flange on the other side due to the shape of the seal face, whereby a problem occurs in a reuse of a flange in some cases. Moreover, since a portion of a concentration of stress is in a convex shape, the portion may be easily damaged, whereby a care and an attention must be paid in handling unfortunately in particular.